Electric valve converting system and excitation apparatus therefor



Sept. 29, 1942. s P, NIXDQRFF 2,297,364

ELECTRIC VALVE CONVERTING SYSTEM AND EXCITATION APPARATUS THEREFOR Filed Oct. 26, 1939 3 Sheets-Sheet l 0 Imvemtorw @I Samuel PNix om fi 611M424 Q mtt orrwey.

Sept. 29, 1942. s. P. NIXDORFF 2,297,364 ELECTRIC VALVE CONVERTING SYSTEM AND EXCITATION APPARATUS THEREFOR Filed Oct. 26, 1939 3 Sheets-Sheet 2 Fig. 4. Fig, 2 I

Inventor: Samuel P Nixdorffi Sept. 29, 1942. s. P. NIXDORFF 2,297,364

ELECTRIC VALVE CONVERTING SYSTEM AND EXCITATION APPARATUS THEREFOR Filed Oct. 26, 1939 3 Sheets-Sheet 3 Inventor: Samuel P Ni dor-ffi D 5 Hi Attovneyh Patented Sept. 29, 1942 ELECTRIC VALVE CONVERTING SYSTEM AND EXCITATION APPARATUS THERE- FOR Samuel P. Nixdorif, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application October 26, 1939, Serial No. 301,421

13 Claims.

My invention relates to electric valve converting systems and more particularly to new and improved apparatus for exciting the control elements of the electric valves of such converting systems.

Heretofore there have been devised numerous electric valve converting systems for transmitting electrical energy between direct and alternating current circuits, direct current circuits of different voltages, or independent alternating current circuits of the same or different frequencies. Many of these systems have included distributor apparatus effective to render conductive the several electric valves in a predetermined sequence to transfer the current between the several terminals of the load circuit of the system. In many cases, however, it is desirable to eliminate the moving contacts and other disadvantages inherent in a mechanical distributing apparatus. My invention relates more particular to an excitation apparatus which may replace the conventional mechanical distributor in the arrangements of the prior art and which eliminates commutation difficulties by virtue of a new and improved control circuit.

It is an object of my invention, therefore, to provide an improved electric valve converting system and an excitation apparatus therefor which will overcome the disadvantages inherent in the mechanical distributor apparatus of the prior art and which will be simple and reliable in operation.

It is another object of my invention to provide a new and improved electric valve converting apparatus.

It is a further object of my invention to provide an improved electric valve converting system and an excitation apparatus therefor which will render conductive the several valves in a predetermined sequence and which will eliminate all moving contacts.

A still further object of my invention is to provide an improved variable frequency electric valve converting system having improved power factor and stable operating characteristics.

Still another object of my invention is to provide a variable frequency electric valve converting system in which the frequencies of the system are controlled in accordance with an electrical condition of the output circuit and in accordance with an electrical condition of the input circuit.

It is another object of my invention to provide a new and improved electric valve converting apparatus in which the short circuits or cross currents between electric discharge valves are substantially eliminated and wherein commutation from one valve to another occurs in proper sequence.

In accordance with one embodiment of my invention I provide an electric valve system for operating a dynamo-electric machine of the synchronous type. The system includes a magnetic commutator comprising an alternating current machine or pilot generator which may be direct connected to the rotor of the dynamo-electric machine for generating an alternating voltage, the frequency of which varies directly with an electrical quantity of the dynamo electric machine. The stator of the pilot generator or auxiliary alternating current machine is energized with alternating current from the input circuit to the main dynamo electric machine and the output of the rotor winding of the pilot generator, which has a frequency proportional to the slip frequency of the machine, is superimposed upon the alternating potential of the input circuit so as to obtain a beat frequency. The term slip frequency as used in connection with the electric valve circuit including a main synchronous type dynamo-electric machine denotes the difference between the supply line frequency and the frequency of the alternating current potential applied to the windings of the synchronous machine through the electric valve translating apparatus. These superimposed alternating current frequencies are rectified in such a manner as to produce an alternating potential of the beat frequency which is also the frequency of rotation of the dynamo electric machine. The electric Valves are provided with both rectifier and inverter excitation of the periodicity of the supply circuit through peaking transformers and he beat frequency obtained from the magnetic commutator is used to allow the rectifier peaks to come on during certain intervals so as to control the proper energization of the electric discharge valves, the rectifier peaks being held off by a D. C. saturating current on the peaking transformer, of the control circuit.

According to another feature of my invention I provide an electric valve system for operating a dynamo-electric machine of the induction type within a range of speeds extending from sub-synchronous operation to over-synchronous operation and a control system very similar to the control system used in connection with the above described synchronous type dynamo-electric machine is provided for obtaining the specified operation of this motor.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, will best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a diagrammatic representation of an electric valve converting apparatus embodying my invention applied to a synchronous type of dynamo-electric machine; Fig. 2 represents certain operating conditions of the apparatus illustrated in Fig. 1; Fig. '3 illustrates an embodiment of my invention as applied to an induction type of dynamo-electric machine; and

Fig. 4 is a modification of the arrangement illustrated in Fig. 3.

Referring now to Fig. 1, I have illustrated therein an electric valve converting apparatus for transmitting energy between alternating current supply circuit l and a variable frequency load circuit comprising a dynamo-electric machine"! l. Although my invention is applicable to any of the electric valve converting systems well known in the art regardless of the number of phases of the load and .supply circuits, for

simplicity of disclosure and explanation I have illustrated an arrangement wherein a quarter- =phase dynamo-electric machine ll of the synchronous type is supplied with electrical energy from a three-phase alternating current source .10. Dynamo-electric machine II is illustrated as having an armature winding comprising a ,plurality of phases l2 and I3, respectively, and a field winding [4 which is energized from any suitable source of direct current l5 through a variable resistor l5. Variable frequency load circuit comprising dynamo-electric machine II is connected to alternating current supply circuit l0 by-means of a transformer I! and aplurality of groups of electric discharge valves I8-25, inclusive. Electric discharge valves [8-25 may be any of the'several types well known in the art and may comprise a plurality of multi-anode, single cathode discharge devices, or as illustrated in thedrawings, they may comprise a plurality of single anode, single cathode valves. Electric discharge valves 18-25, inclusive, are each provided with an anode 26, a cathode 2! and a control electrode or grid 28.

To control the magnitude of the voltage impressed on the :phase windings l2 and E3 of dynamo-electric machine I l and hence to control an operating condition-of the dynamo-electric machine ll, there is provided a suitable arrangement comprising transformer H which is illustrated as a T-connected autotransformer, .the three terminals of which are connected to alternating current supply circuit Hi. This autotransformer comprises two windings 29 and 353, respectively, connected in T relation. Winding .29 of T-connected autotransformer I l is provided with controllable or adjustable contact making mechanisms 3! and 32, whereas windin 30 is provided with adjustable contact making mechanisms 33 and 34, respectively. It will be apparent to those skilled in the art that T-connected auto-transformer l'l may be replaced by any: other suitable type of'static'or dynamic electric power conversion apparatus or adjustable potential-phase transformation means. The midpoint of winding 2-9 of T-connected autotransformer I? is connected to one terminal of phase winding I 2, while the midpoint of winding 38 of T-connected autotransformer I! is connected to one terminal of phase winding I3. The other terminal of phase winding i2 is connected to the midpoint of reactor 35, the purpose of which will be hereinafter described, while correspondingly the other terminal of phase winding [3 is connected to the midpoint of reactor 36. As illustrated in Fig. 1, reactors 35 and 35 are mounted on a common core 3%. The left-hand terminals of reactors 35 and 36 are connected to the cathodes 27 of electric discharge valves 20, 2| and 24, 25, respectively, while the righthand terminals of reactors 35 and 36, respectively, are connected to the anodes 26 of electric discharge valves l8, l9 and 22, 23. The cathode 21 of electric valve l8 and the anode 26 of electric valve 20 are connected to adjustable contact making mechanism 3|, while the cathode 2! of electric discharge valve l9 and the anode 26 of electric discharge valve 2| are connected to adjustable contact making mechanism 32. Similarly, the cathode 2'! of electric discharge valve 22 and the anode 2'5 of electric discharge valve 24 are connected to adjustable contact making mechanism 3'3, while the cathode 2? of electric discharge valve 23 and the anode 25 of electric discharge valve 25 are connected to contact making mechanism 34. It will be observed from the above described circuit that regardless of the direction of current flowing in phase windings l2 and I3, the flow of current through the right and left portions of reactors or inductive impedance devices 35 and 36 will always be from left to right and hence the flux produced in core 36' by virtue of this current will always be induced in a single direction regardless of the direction of energy flow. Therefore induc tive impedance devices or reactors 35 and 3'6 afford little or no impedance to the normal flow of electrical energy in phase windings l2 and 13, but afford a very high impedance to short circuit currents or cross currents between electric discharge valves [8, 26; I9, El; 22, 2:3; or 23, 25, so as not to add to the total reactance of the quarter-phase windings l2 and I 3 of dynamo-electric machine ll. This arrangement of reactors is not my invention but is described and broadly claimed in copending application, Serial No. 332,569, filed April 30, 1940, now Pat. 2,264,854, December 2, 1941, upon an application of Albert H. Mittag, and assigned to the assignee of the present application. This application is a continuation-in-part of Mittag application, Serial N 0. 193,894, filed March 4, 1938.

In order to control the energy transmitted between alternating current circuit IE and dynamo-electric machine ii, there are provided for the electric discharge valves a plurality of excitation circuits El 'M, respectively, each including one of the grids 28 associated with electric discharge valves 23-25, respectively. By means of the excitation circuits the control electrodes or grids 28 of electric discharge valves 1345, respectively, are connected to their cathodes 2'! through current limiting resistors '35, negative bias battery 36 and appropriate windings of grid transformers which will be described in more detail hereinafter. In order to eliminate undesirable high frequency oscillations I provide resistor El and capacitor 58 connected in series relation across the grid to cathode circuits of electric discharge valves ii -2E In order to'control the electric valve converting system to produce the objects noted above there are provided in the excitation circuits 31-5 1, respectively, a plurality of control transformers 49-56, inclusive, to provide inverter excitation for the groups of electric valves H45 and a group of control transformers 51-54, inclusive, to provide rectifier excitation for these discharge paths. Both the rectifier and inverter excitation are of the frequency of the supply circuit l and as is well understood by those skilled in the art the inverter peaks lag the rectifier peaks; the phase displacement being provided by phase shifters 51 and 12. Each of the control transformers 49-56, inclusive, is provided with windings 65 and 65. The secondary windings 6B are the output windings which are connected in the grid to cathode circuits of electric discharge valves 18-25, inclusive. The windings 65 are the primary windings of the control transformers and are energized from the alternating current supply circuit In through any suitable phase shifting arrangement such for example, as rotary phase shifting transformer 61, and transformers 68 and 69. Transformer 69 comprises a T-connected transformer in order to convert the three-phase control potentials to quarter-phase potentials in view of the quarter-phase windings on dynamo-electric machine II. It will, of course, be understood by those skilled in the art that transformer 69 could be eliminated if dynamo-electric machine H were a three-phase machine instead of the quarter-phase arrangement illustrated. It will be observed that the connections to primary windings 65 are so arranged that the grids 28 of valves 18 and 20 are energized 180 electrical degrees out of phase with respect to the grids of valves [9 and 2| and the grids of valves 22 and 24 are energized 180 electrioal degrees out of phase with respect to the grids 28 of valves 23 and 25.

Similarly, the rectifier excitation transformers 51-64, inclusive, are provided with secondary or output windings 10 connected in series with the control electrodes or grids 28 in the respective grid to cathode circuits and primary windings 1| which are the excitation windings energized from the alternating current supply circuit through a suitable phase adjusting means such as rotary phase shifting transformer 12, and transformers 6B and 13, respectively, the latter being a T- connected transformer for converting the threephase control potentials to quarter-phase control potentials. It will be observed that the rectifier excitation on valves I8, 20, 22, and will be 180 electrical degrees out of phase with respect to the excitation on the next adjacent discharge valves I9, 2!, 22 and 23, respectively. In order to prevent a simultaneous flow of current of more than a predetermined magnitude in more than one group of electric valves, which would tend to become a short circuit on one or both of the supply and load circuits, there is provided a means for removing the rectifier excitation from all of the electric discharge valves except the particular ones which transmit energy from supply circuit ID to dynamo-electric machine H. This means comprises the windings 14 which are saturating windings continually energized with direct current for removing the rectifier excitation and which are periodically energized with alternating potentials of the frequency of rotation of dynamo-electric machine H for overcoming the saturation obtained from the direct current energization allowing the rectifier excitation to become effective. Each of the control transformers 49-64, inclusive, is preferably of the self saturating type so that it will become saturated by the energization of the exciting or primary windings 65 or 1!, respectively. The

result is that alternating potentials of a peaked wave form are impressed upon the grids of control electrodes 28 of the several electric discharge valves 18-25. As has been mentioned above the control transformers 51-64 are also designed to become saturated by predetermined currents in another of the exciting windings.

In the arrangement illustrated in Fig. l the rectifier peaks tend to be wiped out all the time and the output of a magnetic commutator, as will be described hereinafter, allows these peaks to become effective periodically in accordance with the rotating speed of dynamo-electric machine H. The saturating windings 14, associated with the excitation circuits 31-40, inclusive, which control the energization of phase winding l2, are serially connected and are energized with direct current obtained across potentiometer 15 through switching means 16 and 11. Unilaterally conductive devices 18 and 19 are provided in series with these saturating windings the purpose of which will become apparent as this description proceeds. Similarly, the saturating windings 14, associated with excitation circuits 4l-44, inclusive, which control the energization of phase winding l3, are serially connected and energized with direct current obtained across potentiometer through switching means 81 and B2. Unilaterally conductive devices 83 and 84 are provided in series with saturating winding 14 associated with excitation circuits 4l-44, inclusive. Potentiometers 15 and 88 may be energized from any suitable source of direct current and in the arrangement illustrated in Fig. 1 I have provided a source of direct current 85 arranged so as to energize potentiometers 15 and at through a variable resistance 86 and switching means 81. By means of potentiometers 15 and 85 and variable resistance 86 the saturation of rectifier excitation transformers 51 to 64 may be controlled so that the saturation may be periodically removed from the transformers associated with certain groups of valves in accordance with the output of the magnetic commutator 83, as will be hereinafter described.

In order to maintain the field winding 14 of dynamo-electric machine H in torque producing relation with armature phase windings I2 and I3 magnetic commutator 88 is provided for periodically allowing the rectifier excitation of the respective valves Iii-25 to become effective. In other words, the magnetic commutator provides means for periodically overcoming the saturating effect of windings 14. Magnetic commutator 88 serves substantially the same purpose as the mechanical distributor of the prior art and comprises a pilot generator 89, the rotor 90 of which is driven at the speed of dynamo-electric machine !i and is illustrated as mechanically coupled therewith. The stator 9| of pilot generator 35 is energized with alternating current from three-phase alternating current source l0 through transformer 68. The output of the rotor 92? of pilot generator 89 is, as will be understood by those skilled in the art, an alternating current having a frequency equal to the slip frequency of the system, or in other words, the difference between the frequency of the potential of the supply line ii} and the frequency of the potential supplied to the windings of dynamo-electric machine i I. This slip frequency output is impressed upon T-ccnnected transformer 92 whereby it is converted to quarter-phase alternating potential proportional to the difference between the frequency of the alternating current supply frequency and the frequency of the alternating current potential impressed on the windings of dynamo-electric machine I I. In order to obtain :an electrical quantity such as an alternating potential which varies in accordance with the speed of the machine II and yet still supplies a potential at standstill conditions of dynamo-electric machine i I, I superimpose the quarter phase slip frequency output of T-connected transformer 92 upon an alternating potential of primary frequency obtained from alternating current circuit 19 through the transformer 68, phase shifting transformer 93 and T-connected transformers 94 and 95. By this arrangement a quarter phase alternating potential having beats is produced. This beat frequency is at all times equal to the frequency of rotation of dynamo-electric machine H and is rectified by means of rectifiers as and 9'! the output of which is impressed across serially connected resistors 98 and 99, respectively,

differentially arranged. The potential appearing across resistor 98 is a direct current potential having the wave shape of the envelope of the beat cycle. The potential across resistor 99 is similar although displaced by 9% electrical degrees in phase. Since these resistors are differentially arranged an alternating potential of the beat frequency'or of a frequency equal to the speed of dynamo-electric machine II is obtained across resistors -93 and 99 which is impressed on the saturating windings 18 associated with the excitation circuits til-54 controlling the energy supplied to phase winding =I3 of dynamo-electric machine I I. When the terminal I99 of resistor 99 is positive relative to terminal I9I a current will flow through unilaterally conductive device 94 aiding the saturating current from potentiometer 89, but unilaterally conductive device 83 prevents this current from flowing therethrough and this potential obtained across terminals I9ii-ltll is such as to counteract the direct current potential obtained from potentiometer 89 and hence remove the saturation of transformers SI and 52 by virtue of direct current from potentiometer 89 whereby the rectifier peaks are no longer wiped out and valves 22 and 23 may transmit current in one direction through phase winding I3. One hundred and eighty electrical degrees later with reference to the rotational frequency of dynamoelectric machine II terminal I9I of resistance 99 is positive relative to terminal I09 of resistance r 98 and the rectifier excitation peaks on grids 23 of electric discharge valves 24 and 25 are allowed to become effective while those of valves 22 and 23 are again held off or removed by saturating windings Id of control transformers SI and 62. Similarly, the output of T-connected transformer 95 is rectified by rectifiers I92 and I93 and impressed upon serially connected resistors I94 and I595 having terminals I95 and I 91. An alternating potential having a frequency equal to the rotational frequency of dynamo-electric machine II is obtained across terminals I96 and I9? and impressed on the saturating windings M of control transformers 51-69 periodically to allow the rectifier peaks to become effective on the control electrodes 28 of electric discharge valves I92I. Phase shifting transformer 93 provides an adjustment for controlling the instant at which the rectifier excitation is allowed to become effective and is analogous to the brush shifting arrangements on the mechanical distributors of the prior art.

In explaining the operation of the electric valve converting system illustrated in Fig. 1, the operation of magnetic commutator 88 will first be described by reference to the curves shown in .Fig.

2. When dynamo-electricmachine II is at standstill the alternating potential impressed upon stator winding 9i of pilot generator 89 is induced by transformer action in rotor winding 99. Therefore, the output of transformer 92 is a quarter-phase output of the same frequency as .is impressed across the primary windings of transformers 9 3 and 95 and by suitably adjusting phase shifter 93 the voltages may be superimposed in such a manner that no voltage occurs across resistor 99, for example, while a direct current voltage occurs across resistor 99. By virtue of rectifiers I 92 and H13 the same will be true across resistors I94 and I95 although the maximum point of the direct current potentials across resistors I 96 and I 95 occurs 90 electrical degrees out of phase with respect to the maximum of the direct current potential across resistors 93 and 99. As dynamo-electric machine I I begins to rotate the frequency appearing across transformer 92 decreases and the superimposed alternating potentials of beat frequency are impressed across rectifiers 99 and 91. The curve A in Fig. 2 represents the resultant alternating potential obtained b superimposing the outputs of transformers 92 and 94 for one particular speed of motor H which is impressed on rectifier 99 while the curve B represents the resultant of the superimposed alternating potential waves impressed on rectifier 9'5. The output of rectifier 96 for the particular speed of motor II mentioned above then becomes a pulsating direct current potential C which is the envelope of the beat cycle and appears as a pulsating direct current potential across resistor 93. The output of rectifier 9? appearing across resistor99lis also a pulsating direct current potential D which is also the envelope of the beat cycle but displaced in phase from C by 99 electrical degrees. Since resistors 98 and 99 are differentially connected the potential appearing across terminals I90 and I9I is the difference of the potentials appearing across resistors 99' and 99, respectively, or the difference between curves C and D,-and is an alternating potential of the beat frequency, that is, having one complete cycle for each beat cycle. This alternating potential appearing across terminals I99 and I M is illustrated by the curve E in Fig. 2. It will of course be understood that the frequency of curve E is the frequency of rotation of dynamo-electric machine I'I. At standstill the frequency is zero, or in other words, a direct current potential is obtained across the terminals I99 and ISI, While at synchronous speed the potential across terminals I99 and I9! is zero. An alternating potential having a frequency equal to the frequency of rotation of dynamo-electric machine II is also obtained across the terminals I 96 and I9? of serially connected resistors I94 and I95, which potential is displaced in phase by 90 electrical degrees from the potential obtained across terminals i 99 and I ill so that control of the quarterphase dynamo-electric machine II may be obtained.

It will be assumed now that dynamo-electric machine II is at standstill and that the switches 16, 11, BI, 82 and 81 are in their closed positions so that the cores of control transformers 57-54 are saturated by virtue of the direct current from source 85. If now alternating current circuit I9 is energized and the phase shifter 93 is adjusted so that the potentials superimposed andappearing at the output of transformer .94 are exactly in phase and equal in magnitude, the potential across resistor 9:8, for example, will be zero while the potential across resistor 99 will be a direct current potential. It will be assumed that potentiometers I5 and 80 as well as resistor 86 have been adjusted so that the direct current potential obtained across terminals I and IOI will be sufficient to overcome the direct current potential causing saturation of the cores of transformers BI and 62, whereby the rectifier excitation peaks of the electric discharge valves 22 and 23 are allowed to become effective and energy is transferred from alternating current circuit I0 to phase winding I3 thereby causing rotation of dynamo-electric machine I I. As dynamo-electric machine II begins to accelerate a very low frequency will be obtained across the terminals I06 and I0! overcoming the saturation caused by the direct current flowing in windings I4 and thereby allowing the rectifier excitation of transformers 51 and 58 to become effective. Electric discharge valves I8 and I9, therefore, will allow energy to be transmitted to phase winding I2, the particular valve I8 or I9 which is conductive depending upon the portion of the cycle of the alternating potential from alternating current circuit I0 since these valves are energized so as to become conductive 180 degrees out of phase with one another. If the speed of dynamo-electric machine I I increases the alternating potentials of the frequency of rotation of dynamo-electric machine II occurring across terminals I00IOI and l06--I6I allow the rectifier peaks impressed upon the control electrode 28 of the various discharge valves I8-25 periodically to become effective in the proper sequence so that a variable frequency alternating potential maybe supplied to phase windings I2 and I3 of dynamo-electric machine Speed control of dynamo-electric machine II may be obtained by the adjustment of rotary phase shifting devices 61 and I2.

My magnetic commutator and electric valve converting system is also applicable for use in connection with the induction type of dynamoelectric machines whereby speed control from subsynchronous speed to oversynchronous speed may be obtained.

In Fig. 3 I have illustrated an electric valve converting apparatus for supplying energy to a variable speed induction motor III having a stator winding H2 energized from a three-phase alternating current source H0 through a threepole switching means H3. The armature of the dynamo-electric machine III is illustrated as comprising quarter-phase windings H4, H5. It will be understood by those skilled in the art that in the case of an induction motor at subsynchronous speeds energy will be taken from phase windings H4, H and returned to three-phase alternating supply circuit IIO by means of the electric valve converting apparatus while at or above synchronous speed energy will be supplied from alternating current circuit H0 through the electric valve converting apparatus to phase windings H4 and H5. The electric valve converting apparatus and control circuits therefor illustrated in Fig. 3 are in most respects identical with those illustrated in Fig. 1 and the corresponding parts are indicated by the same reference numerals. Potentiometers 15 and 80 for supplying direct current to saturating windings I4 of grid transformers 5144, respectively, are energized with direct current from suitable direct current generators H6 and H7, respectively, the

generators being driven by electric motors H8 7 and H9, respectively, energized with alternating current from alternating current source H0 through transformer 68.

The magnetic commutator I20 provided for the induction type dynamo-electric machine III of Fig. 3 must function differently in certain respects than the magnetic commutator of Fig. 1, as will be understood by those skilled in the art. This magnetic commutator must control the effectiveness of the rectifier excitation relative to the slip frequency of dynamo-electric machine III as contrasted with Fig. 1 where control in accordance with rotational frequency was provided. In order to obtain an electrical quantity proportional to the slip frequency of dynamoelectric machine III I provide a pilot generator I2I, the rotor winding of which is directly coupled to and driven by dynamo-electric machine III. Pilot generator I2I is preferably a variable speed polyphase alternating current commutating motor of the type described and broadly claimed in United States Letters Patent Reissue 14,031, granted December 14, 1915, upon an application of H. K. Schrage. This polyphase commutator pilot generator comprises a rotor Winding I22 supplied with three-phase alternating current through rotary phase shifting transformer I23 and transformer 68 from alternating current source H0. In addition to primary winding I22 pilot generator I2I also comprises secondary windings I24, I25, I26 and I21, respectively, and adjusting winding I28. Quarterphase slip frequency alternating potentials are obtained from pilot generator I2I across terminals I29, I30 and I3I, I32, respectively. It will be understood that at standstill conditions of dynamo-electric machine III the alternating potential obtained across terminals I29, I30 and I3I, I32, are of the frequency of alternating current supply circuit IIO while when dynamo-electric machine I I I is rotating at synchronous speed a direct current potential will be obtained across these respective terminals. Above synchronous speed, of course, the phase of the alternating potentials of slip frequency will be displaced in phase by degrees as compared with these potentials at subsynchronous speeds. The operation of the electric valve converting system will be substantially the same as that described for Fig. 1 and. will be well understood by those skilled in the art. When dynamo-electric machine III is started from standstill switch H3 is moved to the closed position and electric discharge valves I8-25 operate sequentially as inverters to transfer electrical energy induced in phase windings H4 and H5 back to alternating current supply line IIO. Below synchronous speeds speed control may be obtained by virtue of contact making mechanisms 3| to 34, inclusive, the higher speed being obtained by decreasing the counter electromotive force against which the electric discharge valves I 8-25 must operate as inverters. This is obtained by moving the contact making mechanisms 3I-34 as near to the center of the respective windings 29 and 30 as possible. Speed control as well as power factor control may also be obtained by suitably adjusting phase shifting transformers 61 and I2. From zero speed up to some speed below synchronism magnetic commutator I20 is not essential except as regards the transfer of the wattless energy component since the electric discharge valves I8 to 25 operate as inverters and in view of the voltage conditions would not operate as rectifiers even if the rectifier excitation were allowed to become effective by virtue of magnetic commutator lit; However,

nating current circuit lie to phase windings Hi6 and H and as the slip frequency decreases on approaching synchronous speed a low freq alternating current component from commutator l28 periodically allows the re excitation to become effective upon the cont electrodes of the respective discharge valves in proper sequence. When synchronous speed is attained direct current components of control potential are obtained from magnetic commutator I28 so that the phase windings I I6 H5 are energized with direct current through electric discharge valves l2-25. Above synchronous speed the components. of control potential obtained from magnetic commutator i253 causes the apparatus to function in identically the same manner. as the synchronous type dynamo-electric machine l I described in connection with Fig. l.

. In Fig. "4 I have illustrated only a portion of the electric valve converting apparatus shown in Fig. 3 wherein the magnetic commutator E29 has been replaced by the same type of magnetic commutator 88 illustrated in Fig. 1. Furthermore, instead of direct current generators lit ill for supplying the direct current for saturating windings M I provide the same source of supply 85 as illustrated in Fig. l, the corresponding parts being indicated by the same reference numerals.

However, in this case, the stator winding 6! of the pilot generator 89 is energized with direct current as contrasted with 1 where an alternating current was supplied thereto. By energizing the stator of pilot generator with direct current an alternating potential will be obtained across the terminals of resistors 98, 5t and let, I55, respectively, which is proportional to slip frequency rather than the rotational frequency as in the case of the synchronous motor type of dynamo-electric machine ll illustrated in Fig. 1. Commutator 83 of Fig. 4 operates identically insofar as output control potentials are concerned, as commutator l2i5 illustrated in 3 and its operation will be well understood by those skilled in the art in view of the detailed description included above.

While I have described certain particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and 'modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an lternating current circuit, a second alternating current circuit, electric translating apparatus connected between said circuits for transmitting power therebetween and comprising a plurality of electric valve means each having a control member for conrolling the conductivity thereof, an excitation circuit for energizing said control members comprising means for impressing both a rectifier and an inverter component of excitation on said control members to excite said valve means for both rectifier and inverter operation with respect to said first mentioned circuit, means for normally maintaining said rectifier excitation ineffective, and means for periodically allowing said rectifier excitation to become effective at the periodicity of said second mentioned circuit to render said electric valve means conductive in a predetermined order to effect transfer of'power between said first mentioned and said second alternating current circuit.

2. In combination, an alternating current supply circuit, a variable frequency alternating current load circuit, electric translating apparatus members comprising means for impressing both a rectifier and an inverter component of excita v tion on said control members to excite said valve means for both rectifier and inverter operation with respect to said supply circuit, means for normally removing said rectifier excitation and means comprising a magnetic commutator for periodically allowing said rectifier excitation tobecome effective at the periodicity of said load circuit to render said electric valve means conductive in a predetermined order to effect transfer of power between said supply and load circuits.

3. In combination, an alternating current circuit, a second alternating current circuit, electric translating apparatus connected between said circuits for transmitting power therebe-- tween and comprising a plurality of electric valve means each having a control member for controlling the conductivity thereof, an excitation circuit for energizing said control members comprising means for impressing both a rectifier and an inverter component of excitation on said control members to excite said electric valve means for both rectifier and inverter operation with respect to said supply circuit, means for normally maintaining said rectifier excitation ineffective, means for producing'a periodic voltage which varies in accordance with an electrical condition of one of said circuits, means for producing a second periodic voltage the frequency of which variesin accordance with a controlling influence derived from the other of said circuits,

and means responsive to a periodic voltage of beat frequency produced by said periodic voltages for allowing said rectifier excitation to become eifective at the periodicity of said second mentioned alternating current circuit to render said electric valve means conductive in a predetermined order to effecttransfer of power between said first mentioned and said second alternating current circuits. I

4, In combination, an alternating current circuit, a second alternating current circuit, electric translating apparatus connected between said circuits for transmitting power therebetween and comprising a plurality of electric Valve means each having a control'member for controlling the conductivity thereof, an excitation circuit forenergizing said control members comprising means for impressing botha rectifier and an inverter component of excitation on said control members to excite said valve means for both rectifier and inverter operation with respect to said supply circuit, means for normally maintaining said rectifier excitation ineffective and means for producing a beat frequency alternating current potential modulated in accordance with the voltage of said second alternating current circuit for periodicall allowing said rectifier excitation to become effective to render said electric valve means conductive in a predetermined order to effect transfer of power between said first mentioned and said second alternating current circuits.

5. In an electric valve converting system, an alternating current supply circuit, a variable frequency alternating current load circuit, translating apparatus connected between said circuits for transmitting power therebetween and com prising a plurality of electric valve means each having a control member for controlling the conductivity thereof and an excitation circuit for energizing said control member comprising means for successively exciting said control members for rectifier operation at the periodicity of said alternating current supply circuit, means for normally maintaining said rectifier excitation ineffective and means comprising a magnetic commutator for allowing the rectifier excitation to become effective periodically at the frequency of said load circuit.

6. In an electric valve converting system comprising a supply circuit, a load circuit, means including a plurality of electric valves for transmitting energy therebetween, each of said valves being provided with a control electrode, excitation apparatus for said electrodes comprising a control circuit for each of sad valves including a saturable core transformer winding, means for exciting the transformer grinding with an alternating potential of the frequency of said first mentioned alternating current circuit, means for normally saturating the cores of said transformer windings to nullify the excitation of said transformer windings, and means responsive to the frequency of said second mentioned alternating current circuit for overcoming the saturation of the cores of said transformer windings to allow said excitation current to become effective thereby rendering said electric valve means conductive in a predetermined order to effect a transfer of power between said first mentioned and said second alternating current circuits.

7. In an electric valve converting system, an alternating current circuit, a second alternating current circuit, electric translating apparatus connected between said circuits for transmitting power therebetween and comprising a plurality of electric valve means each having a control member for controlling the conductivity thereof, excitation apparatus for said control electrodes comprising means for impressing upon said electrodes an alternating potential of the frequency of said first mentioned alternating current circuit and of peaked wave form to excite said valve means for inverter operation, a saturable core transformer winding included in the circuit of the control electrode of each of said valve means, means for inducing in said transformer winding an alternating potential of the frequency of said first mentioned alternating current circuit for exciting said valve means for rectifier operation and a saturating winding for each of said transformer cores connected to carry a direct current for normally removing the rectifier excitation from said control electrodes, and means for periodically allowing said rectifier excitation to become effective at the periodicity of said second mentioned alternating current circuit to render said electric valve means conductive in a predetermined order to effect transfer of power between said first mentioned and said second alternating current circuits.

8. An electric valve converting system comprising an alternating current circuit, a second alternating current circuit, means including a plurality of groups of electric valves for transmitting energy therebetween, means for exciting said groups of valves for inverter operation to transmit energy from said second alternating current circuit to said first mentioned alternating current circuit, means for simultaneously exciting said groups of valves for rectifier operation, means continuously tending to remove the rectifier excitation from said groups of valves, and means responsive to the frequency of said second mentioned alternating current circuit for periodically and successively allowing the rectifier excitation to become effective to render said groups of valves conductive in a predetermined order to effect transfer of power between said first mentioned and said second alternating current circuits.

9. In an electric valve converting system comprising an alternating current supply circuit, a variable frequency alternating current load circuit, means including a plurality of groups of electric valves for transmitting energy therebetween, each of said valves being provided with a control electrode, excitation apparatus for said electrodes comprising means for energizing said control electrodes with a component of said al' ternating current supply circuit of peaked wave for normally exciting said valves for inverter operation, a saturable core transformer winding included in the circuit of the control electrode of each of said valves, means for inducing in said transformer winding an alternating potential of the frequency of said supply circuit for exciting said valves for rectifier operation, saturating windings for said transformer cores, means for continuously exciting said saturating windings with direct current to remove the rectifier excitation from said control electrodes, and means responsive to the frequency of said alternating current load circuit for producing a potential for periodically overcoming said saturating means and allowing said rectifier excitation to become effective at the periodicity of said alternating current load circuit thereby rendering said electric valves conductive in a predetermined order to effect the transfer of power between said supply and load circuits.

10. In combination, an alternating current circuit, a second alternating current circuit, electric translating apparatus connected between said circuits for transmitting power therebetween and comprising a plurality of electric valve means each having a control member for controlling the conductivity thereof, and an excitation system for energizing the control member comprising means for impressing on the control members a plurality of periodic voltages of a periodicity corresponding to that of said first mentioned circuit to excite said valves for both rectifier and inverter operation with respect to said first mentioned circuit, means for normally maintaining one of said periodic voltages ineffective and means for periodically allowing said periodic voltage to become effective at the periodicity of said second mentioned circuit to render said electric valve means conductive in a predetermined order to effect a transfer of power between said first mentioned and said second alternating current circuits.

11. In combination, an alternating current supply circuit, a dynamo-electric machine, electric translating apparatus connected between said alternating current circuit and said dynamo-electric machine for transmitting power therebetween and comprising a plurality of electric Valve means each having a control member for controlling the conductivity thereof, and an excitation system for energizing the control member comprising means for impressing on the control member a plurality of periodic voltages of a periodicity corresponding to that of said alternating current circuit, means for normally maintaining one of said periodic voltages ineffective and means for generating a voltage having the rotational frequency of said dynamoelectric machine to periodically overcome said last mentioned means to render said electric valve means conductive in a predetermined order to effect transfer of power between said alternating current circuit and said dynamo-electric machine,

12. In an electric valve converting system, an alternating current circuit, a dynamo-electric machine provided with a plurality of phase windings, electric translating apparatus connected between said alternating current circuit and said phase windings for transmitting power therebetween and comprising a plurality of electric valve means each having a control member for controlling the conductivity thereof, an excitation circuit for energizing the control member comprising means for impressing on the control member a plurality of periodic voltages of a periodicity corresponding to that of said alternating current circuit, means for normally maintaining one of said periodic voltages inefiective, a pilot generator driven by said dynamo-electric machine for producing a periodic voltage which varies in accordance with an electrical condition of said dynamo-electric machine, means for superimposing the potential produced by said pilot generator upon a potential obtained from said alternating current circuit to produce a periodic voltage of beat frequency, means for converting said periodic voltage of beat frequency into a periodic voltage of the rotational frequency of said dynamo-electric machine for causing said normally inefiective periodic voltage of said excitation circuit to become effective to render said electric valve means conductive in a predetermined order thereby to effect the transfer of power between said alternating current circuit and said dynamo-electric machine.

13. In combination, a supply circuit, an alternating current dynamo-electric machine, electric translating apparatus connected between said supply circuit and said dynamo-electric machine for transmitting power therebetween and comprising an electric valve frequency changer including a plurality of electric valve means each having a control member for controlling the conductivity thereof, an excitation system for energizing said control member including a second dynamo-electric machine having a winding energized from said supply circuit and a rotatable element driven by a rotatable element of said first dynamo-electric machine for producing a control potential having a frequency equal to the beat frequency of said supply frequency and the rotational frequency of said first mentioned dynamo-electric machine to control the operation of said electric valve frequency changer in accordance with an operating condition'of said machine.

SAMUEL P. NIXDOR-FF. 

